1. Field
The disclosure relates to a mechanical drum brake, and more particularly to a mechanical drum brake capable of smoothly returning brake shoes to the initial position thereof when braking is released.
2. Description of the Related Art
In general, a mechanical drum brake provides braking force by causing friction between a brake shoe with linings and a drum by using a cable linked with a parking brake lever.
When such a mechanical drum brake is used as a parking brake of a vehicle, the mechanical drum brake is paired with a disc brake to brake a rear wheel through hydraulic pressure, called a DIH (Drum In Hat) type.
As shown in FIG. 1, the mechanical drum brake includes a back plate 2 coupled with a vehicle body and a pair of brake shoes 3a and 3b operating outward by an actuation lever 10, which is described later, such that a drum 1 rotating together with a wheel is restricted at the front of the back plate 2.
The brake shoes 3a and 3b having linings 6a and 6b attached thereto are rubbed against an inner circumferential surface of a drum 1 to generate braking force in braking. The brake shoes 3a and 3b are classified into the primary shoe 3a, which is provided in a forward-rotation direction of the drum 1, and the secondary shoe 3b, which is opposite to the primary shoe 3a, about an anchor pin 7.
The brake shoes 3a and 3b include rims 5a and 5b having a semicircular shape having the linings 6a and 6b attached thereto and webs 4a and 4b coupled with inner circumferential surfaces of the rims 5a and 5b to support the rims 5a and 5b. In this case, the webs 4a and 4b of the brake shoes 3a and 3b have one end supported by the anchor pin 7 while making contact with the anchor pin 7 and an opposite end supported by an adjuster 9 while making contact with the adjuster 9.
The adjuster 9 connects the opposition ends of the primary shoe 3a and the secondary shoe 3b with each other and compensates for the increase of the gap between the linings 6a and 6b and the internal circumferential surface of the drum 1 caused by the abrasion of the linings 6a and 6b due to the continuous braking.
Conventionally, when the brake is operated, braking force of the primary shoe 3a making contact with the anchor pin 7 and the secondary shoe 3b making contact with the adjuster 9 is maximized.
The two brake shoes 3a and 3b intend to rotate in one direction upon the braking operation, so the brake shoes 3a and 3b are biased toward the secondary shoe 3b. 
Accordingly, after the braking has been released, the primary and secondary shoes 3a and 3b are returned to the initial positions thereof with respect to the anchor pin 7. However, the positions of the first and second shoes 3a and 3b are returned in a state in which the positions are biased to the side of the secondary shoe 3b. Therefore, the smooth position returning is not achieved.